1. POWER QUALITY ISSUE WITH GRID CONNECTED WIND ENERGY SYSTEM
Ravijesh Kumar
Department of Electrical and Electronics Engineering
School of Engineering and Technology
Sharda University, Gr. Noida, UP, INDIA
ravijesh35@gmail.com
ABSTRACT: The Wind energy sources, which have been expected to be a promising
alternative energy source, can bring new challenges when it is connected to the power grid.
However, the generated power from renewable energy source is always fluctuating due to
environmental condition. In the same way Wind power injection into an electric grid affects the
power quality due to the fluctuation nature of the wind and the comparatively new types of its
generators. On the basis of measurements and norms followed according to the guide lines
specified in IEC-61400 (International Electro-technical Commission) standard, the performance
of the wind turbine and there by power quality are determined. The power arising out of the wind
turbine when it connected to grid system concerning the power quality measurements are-the
active power, reactive power, voltage sag, voltage swell, harmonics, and electrical behaviour of
switching operation and these are measured according to national/international guidelines. The
paper clearly shows the existence of power quality problem due to installation of wind turbine
with the grid. In this proposed scheme a FACTS device that is STATIC COMPENSATOR
(STATCOM) is connected at a point of common coupling with a battery energy storage system
(BESS) to reduce the power quality problems. The battery energy storage system is integrated to
support the real power source under fluctuating wind power. The FACTS Device control scheme
for the grid connected wind energy generation system to improve the power quality is simulated
using MATLAB in power system block set. The intended result of the proposed scheme relives
the main supply source from the reactive power demand of the load and the induction generator.
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2. 1.INTRODUCTION: To have sustainable growth and social progress, it is necessary to meet
the energy need by utilizing the renewable energy resources like wind, biomass, hydro, co-generation,
etc. In sustainable energy system, energy conservation and the use of renewable
source are the key paradigm. The need to integrate the renewable energy like wind energy into
power system is to make it possible to minimize the environmental impact on conventional plant.
The integration of wind energy into existing power system presents technical challenges and that
requires consideration of voltage regulation, stability, power quality problems. The power quality
is an essential customer-focused measure and is greatly affected by the operation of a distribution
and transmission network. The issue of power quality is of great importance to the wind turbine.
Today, more than 28 000 wind generating turbines are successfully operating all over the world.
In the fixed-speed wind turbine operation, all the fluctuation in the wind speed are transmitted as
fluctuations in the mechanical torque, electrical power on the grid and leads to large voltage
fluctuations. The power quality issues can be viewed with respect to the wind generation,
transmission and distribution network, such as voltage sag, swells, flickers, harmonics etc.
However the wind generator introduces disturbances into the distribution network. One of the
simple methods of running a wind generating system is to use the induction generator connected
directly to the grid system. When the generated active power of an induction generator is varied
due to wind, absorbed reactive power and terminal voltage of an induction generator can be
significantly affected. A proper control scheme in wind energy generation system is required
under normal operating condition to allow the proper control over the active power production.
In the event of increasing grid disturbance, a battery energy storage system for wind energy
generating system is generally required to compensate the fluctuation generated by wind turbine.
A STATCOM based control technology has been proposed for improving the power quality
which can technically manages the power level associates with the commercial wind turbines.
2.POWER QUALITY IMPROVEMENT
1) International electro technical commission guidelines: some guidelines of
measurements and norms are specified under IEC 61400 standard which determines the power
quality of wind turbines.
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3. I. IEC 61400-21: Measuring the power quality characteristic of grid connected wind
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turbine.
II. IEC 61400-13: Wind Turbine—measuring procedure in determining the power
behavior.
III. IEC 61400-3-7: Measures the emission limits for fluctuating load and IEC 61400-12:
Wind Turbine performance.
2) Harmonics: It is due to the operation of power electronic converters. Harmonic voltage and
current should be in limited as per the IEC-61400-36 guideline. The rapid switching gives a large
reduction in lower order harmonic current and higher order harmonics are filtered out by using
filters.
3) VOLTAGE VARIATION: This is due to the fluctuations in the wind turbine due to wind. The
voltage variation is directly related to real and reactive power variations. The voltage variation is
commonly classified as under:
• Voltage Sag/Voltage Dips.
• Voltage Swells.
• Short Interruptions.
• Long duration voltage variation.
The voltage flicker issue describes dynamic variations in the network caused by wind turbine or
by varying loads. Amplitude of voltage fluctuations depends on grid strength, network
impedance, phase angle and power factor of wind turbine. During voltage variations frequency is
in the range 10–35 Hz. The IEC 61400-4-15 specifies a flicker meter that can be used to measure
flicker directly.
4) WIND TURBINE LOCATION IN POWER SYSTEM: It is located where the power quality is
highly influenced. Its operation and its influence on the power system depend on the structure of
the network.
5) SELF EXCITATION OF WIND TURBINE GENERATING SYSTEM: The self-excitation of
wind turbine generating system arises a risk equipped with commutating capacitor. It provides

4. the reactive power compensation to the induction generator. The disadvantages of self-excitation
are the safety aspect and balance between real and reactive power.
6) CONSEQUENCES OF THE ISSUES: Voltage variations, voltage flicker, harmonics causes
the malfunctions of equipments. It leads to tripping of protection devices, damaging the sensitive
equipments. Overall it degrades the power quality in the grid.
GRID COORDINATION RULE: American Wind Energy Association led the effort to develop
its own grid code for stable operation as per IEC-61400-21 for the interconnection of wind plants
to the utility systems, after the blockout in United State in August 2003. According to these,
operator of transmission grid is responsible for the organization and operation of interconnected
system.
1) Voltage rise (u): The voltage rise at the point of common coupling can be approximated
as a function of maximum apparent power Smax of the turbine, the grid impedances R
and X at the point of common coupling and the phase angle ,
given in Eq. 1.
휟햚 = smax (RcosΦ-XsinΦ) / 햚²
Where 휟햚 —voltage rise, smax —max. apparent power,
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Φ—phase difference,
U—nominal voltage of grid.
The Limiting voltage rise value is <2 %
2) The voltage dips: The voltage dips is due to startup of wind turbine and it causes a
sudden reduction of voltage. It is the relative % voltage change due to switching
operation of wind turbine. The decrease of nominal voltage change is given in Eq.
D = Ku sn/sk
Where d is relative voltage change,
sn is rated apparent power,
sk is short circuit apparent power, and

5. [5]
Ku is sudden voltage reduction factor.
The acceptable voltage dips limiting value is <3%.
3) Harmonics: The harmonic distortion is assessed for variable speed turbine with a
electronic power converter at the point of common connection. The total harmonic
voltage distortion of voltage is given as in Eq.
4) GRID FREQUENCY: The grid frequency in India is specified in the range of 47.5–51.5
Hz, for wind farm connection.
3. TOPOLOGY FOR POWER QUALITY IMPROVEMENT
The STATCOM based current control voltage source inverter injects the current into the grid
will cancel out the reactive part and harmonic part of the load and induction generator current,
thus it improves the power factor and the power quality. To accomplish these goals, the grid
voltages are sensed and are synchronized in generating the current. The proposed grid connected
system is implemented for power quality improvement at point of common coupling (PCC), for
grid connected system.

6. BY USING STATCOM – STATIC SYNCHRONOUS COMPENSATOR
The STATCOM (or SSC) is a shunt-connected reactive-power compensation device that is
capable of generating and/ or absorbing reactive power and in which the output can be varied to
control the specific parameters of an electric power system. In general it is solid state switching
converter which is capable of generating or absorbing independently controllable real and
reactive power at its output terminals when it is fed from an energy source at its input terminals.
Specifically, the STATCOM considered in this is a voltage-source converter from a given input
of dc voltage produces a set of 3-phase ac-output voltages, each in phase with and coupled to the
corresponding ac system voltage through leakage reactance. The dc voltage is provided by an
energy-storage capacitor.
 It is a Regulating device used on AC Transmission networks.
 It is based on a Voltage-Source converter.
 It acts in either Capacitive (or) Inductive mode
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7. A STATCOM can improve power-system performance in such areas as the following:
1. The dynamic voltage control in Transmission and distribution systems;
2. The power-oscillation damping in power transmission systems;
3. The transient stability;
4. The voltage flicker control; and
5. It also controls real power in line when it is needed.
Advantages:
1. It occupies small areas.
2. It replaces the large passive banks and circuit elements by compact converters.
3.Reduces site work and time.
4. Its reponse is very fast.
3phase output current and voltage of grid
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8. 6-pulse statcom ouput current and voltage
4. CONCLUSION
we present the FACTS device (STATCOM) -based control scheme for power quality
improvement in wind generating system on integration to the grid and with nonlinear load. The
power quality issues and its consequences on the consumer and electric utility are presented. The
operation of the control system developed for the STATCOM in MATLAB/SIMULINK for
maintaining the power quality is to be simulated. It has a capability to cancel out the harmonic
parts of the load current. It maintains the source voltage and current in-phase and support the
reactive power demand for the wind generator and load at PCC in the grid system, thus it
enhance the utilization factor of transmission line. The integrated wind generation and FACTS
device with BESS have shown the outstanding performance. Thus the proposed scheme in the
grid connected system fulfills the power quality norms as per the IEC standard 61400-21.
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9. [9]
4.Bibliographic information:
1. S. Heier, Grid Integration of Wind Energy Conversions. Hoboken, NJ: Wiley, 2007.
2. A STATCOM-Control Scheme for Grid Connected Wind Energy System for Power Quality
Improvement Sharad W. Mohod, Member, IEEE,
3. http://en.wikipedia.
4. M. Tsili and S. Papathanassiou, ―A review of grid code technology requirements for wind
turbine,‖ Proc. IET Renew. Power gen., vol. 3, pp. 308–332, 2009.